Its not just the comment though, theres a significant amount of other Metadata like the app that it was sent from, timestamp within the track, splits, etc. My understanding is lnurlp is character limited?

So thats where nostr comes in. Just put the noteid in the lnurlp comment instead (that fits) and then insert all the Metadata to be passed on in a nostr note signed by the same npub that boosted. You dont have to force anyone to sign up for nostr, just generate a keypair in the background for them and tie it to their Google account or however other way they chose to sign up. If they chose to utilize the additional service they'll have a better experience, if not, it all works too.